1. Field of the Invention
The present invention relates to bisazo and trisazo compounds for use in optical information recording media, a bis(diazonium) salt which is an intermediate for producing the bisazo compound, and methods of producing the same.
2. Discussion of Background
Development of an optical disc recording apparatus, as means for recording information with high recording density, has recently become very active. Optical information recording media, which are used for the optical recording apparatus, have feature that the recording media are not easily worn out, because writing and reading are performed by a non-contact operation with a thermal head, and moreover recording can be carried out with high density. Development of various kinds of optical information recording media is also in progress.
Among such optical recording media, development of a heat-mode recording medium is particularly active. The heat-mode optical information recording medium utilizes recording light by conversion of the light to the thermal energy. A pit-formation type optical information recording medium is an example of the above-mentioned heat-mode recording medium. More specifically, in the pit-formation type recording medium, a portion of the optical information recording medium is melted by the application of recording light course such as a laser beam thereto, and the melted portion is removed, whereby small holes called pits are formed on the recording medium in the writing operation. Information is recorded by formations of pit, and the information is read by detecting the pits under application of reading or reproduction light.
A variety of other optical information recording media such as an optical information recording medium utilizing phase changes and an optical information recording medium utilizing photochromic materials have been proposed.
An optical information recording medium is required for the efficient absorption of light energy applied by a laser beam. Therefore, it is necessary to employ an optical information recording medium with high absorbance with respect to a laser beam with a specific wavelength for information recording. It is also necessary that the recording medium have high reflectance to a laser beam with a specific wavelength in order to accurately reproduce recorded information.
Most of conventional pit-formation type optical information recording media comprise materials based on the main components inorganic materials such as Se and Te. However, it is reported that recording media comprising an organic material consisting essentially of an organic dye in a recording layer are recently used more than the recording media based on inorganic materials. This is because there are environmental pollution problems with the inorganic materials and recording media with high sensitivity are required.
Examples of the organic dyes used for recording media are cyanine dyes (disclosed, for example, in Japanese Laid-Open Patent Application 58-114989), metal complexes (disclosed, for example, in Japanese Laid-Open Patent Application 58-16888), and phthalocyanine dyes (disclosed, for example, in Japanese Laid-Open Patent Applications 3-43461 and 3-77840).
Some of these dyes employed in the optical information recording media are satisfactory with respect to the absorption wavelength when a semiconductor laser is used. However, the above dyes are unstable for oxygen and humidity when preserved in contact with air, the solubilities of these dyes are low, and the sensitivities of the recording media using these dyes are also low. Thus, satisfactory organic dyes for use in optical information recording media are still few.